Below is a copy of patent for the meta bromination of benzaldehyde. It claims a 89% yield. Yes it is only a patent but there is a similar method on
PrepChem which has less detail. The patent gives options for the poly chloroalkane solvent such as dichloromethane or chloroform that are more easily
obtained than 1,2-dichloroethane given by PrepChem.
Below are the equations for the above bromine/chlorine method which is unusual for me. I don't know if it produces a higher yield than only using
bromine.
The above is a snip from this preparation
Attachment: continousproductionmbb.pdf (265kB) This file has been downloaded 250 times
karlos³ - 21-2-2022 at 20:26
Well, we know that orgsyn can be trusted greatly, and they give enough details to make it repeatable.
There is this procedure, with a 59% yield for 3-bromobenzaldehyde: http://orgsyn.org/demo.aspx?prep=CV5P0117RustyShackleford - 22-2-2022 at 10:08
Below are the equations for the above bromine/chlorine method which is unusual for me. I don't know if it produces a higher yield than only using
bromine.
The above is a snip from this preparation
Its most likely done that way for better atom economy on the bromine, chlorine is a lot less expensive afterall. wg48temp9 - 22-2-2022 at 11:24
Well, we know that orgsyn can be trusted greatly, and they give enough details to make it repeatable.
There is this procedure, with a 59% yield for 3-bromobenzaldehyde: http://orgsyn.org/demo.aspx?prep=CV5P0117
Thanks for that. I suspect the Br/Cl method may be designed to save bromine by using half Br and half Cl. I don't need to minimise Br usage and I
prefer not have to use Cl gas.wg48temp9 - 23-2-2022 at 02:09
As I don't have benzaldehyde, I could make it from the toluene that I do have a few 100ml of but I decided to purchase some benzaldehyde.
So while I am waiting for the benzaldehyde to arrive I thought I would consider using NBS or the hydantoin version or Br2+Br2/Cl2. But its more
complicated than I thought.
I have to go out now and there are a lot power outs at the moment so I will post this now and add my thoughts later.
Ideally for its simplicity I would like to use NBS in a polar chlorinated solvent. Unfortunately I don't have sufficient knowledge to know if that
would work.
The obvious problem is the limited solubility of NBS in a polar chlorinated solvents. Perhaps THF could be used.
I don't understand how the reaction would get going. Apparently HBr, light or a peroxide can start the reaction. I do have HBr acid but i suspect
that can not be used due to its water content. Light initiation would be ideal if a 60W quartz tungsten halogen lamp would be sufficient. I also have
some peroxide catalyst for resin.
Also I would like to use FeBr3 perhaps made in situ,
